Historically, the RADTRAD-NAI solver is derived from version 3.01 of the RADTRAD solver, which was prepared at Sandia National Laboratory. Changes were implemented to make the RADTRAD-NAI solver conform to version 3.02 of the RADTRAD solver. Several significant contributions have been made by NAS. First, the source code was brought into a code control system under NAS's QA program to assure that future development and maintenance would be performed according to the requirements of 10CFR50, Appendix B. Second, the code package was subjected to a design review to document the status of the code, as received. The design review evaluated the accuracy and completeness of the code and documentation. This included verification of the consistency of the code with respect to referenced information and verification of the consistency of the code with respect to code documentation. The design review also involved validation, with particular emphasis on evaluation of models that allowed specific code features to be isolated, thereby facilitating comparison of results to known solutions. As a result of the design review and subsequent analyses, several errors were identified in the solver. These errors have been corrected and were presented to the distributors of the RADTRAD code package. Third, clear, complete and orderly line-by-line input instructions were written to facilitate preparation of input.

RADTRAD-NAI further extends the capabilities of the NRC released RADTRAD Version 3.01 by providing new features, improved output files, increased user-friendly features and a web-based interface. Examples of improvements include:

• Correction of identified errors in RADTRAD, as described in our Error Report to the NRC
• Correction of identified errors in RADTRAD Versions provided by other Vendors
• Correction of identified errors in Worst Two-Hour Dose Calculation
• Development of the web-based user interface that allows qualified users to access the code on our web server, relieving the end users of the responsibility of installing and maintaining a QA rated code
• Addition of capability to track pH level in suppression pools/sumps
• Addition of capability to vary the free volume in a compartment with time (e.g., to account for water level variation in steam generators)
• Addition of capability to delete compartments, flow paths, etc. with the web-based GUI
• Addition of capability to include more inputs on each menu
• Addition of capability to track decay and release of noble gases from filters
• Simplification of the decay/daughtering flag scheme
• Improvement of output file structure and reporting